Airborne station for aerial observation system

ABSTRACT

An airborne radar station, hovering at a fixed location above an associated ground station, comprises a supporting section with a gyrostabilized body held aloft by helicopter blades and a supported section suspended from that body for independent rotation about a substantially vertical axis. The coupling between the two sections includes a parallelogrammatic linkage with an upper base secured to (or part of) the body and a lower base rigid with the supported section or secured thereto through an adjustable mounting automatically maintaining the verticality of a suspension shaft for that section. The downdraft generated by the swirling rotor blades acts upon adjustable fins on the supported section to rotate the latter at a rate controlled by a governor and by signals from the ground station which also includes a tracking radar trained upon the airborne station to determine deviations from its assigned position in space, such deviations giving rise to corrective signals transmitted by short waves to the airborne station for altering the attitude of the supporting section and the effectiveness of its blades by changing the direction of thrust of one or more jets of compressed air issuing from the tip of each blade. A radar antenna on the rotating supported section scans the surrounding area, especially in the region close to the ground, and retransmits incoming echo signals to receiving equipment at the ground station.

United States Patent [72] Inventors Henri Billottet Fontenay Aux Roses;7 Marcel Kretz, Paris, both of France {21] Appl. No. 796,234 22 FiledFeb. 3, 1969 [45] Patented Oct. 5, 1971 [731 Assignees CompagnleFrancaise Houston-Hotchkiss Brandt Paris, France; Giravions DurandSuresnes, France, part interest to each [32] Priority Feb. 1, 1968, Dec.26, 1968 [33] France [31] 138,277 and 180,638

[54] AIRBORNE STATION FOR AERIAL OBSERVATION SYSTEM 17 Claims, 7 DrawingFigs.

[52] US. Cl 343/6 R, 244/17.1 244/17.17, 244/17.25, 343/65 R 51 Int. Cl.1 G01s 9/02, B64 c 25/00 [50] Field of Search 343/6, 6.5;244/17.15,17.11,17.25,17.17;l70/135.4

[56] References Cited UNITED STATES PATENTS 1,526,657 2/1925 Bea 244/17.11 1,652,090 12/1927 Calvert 244/l7.15 2,001,529 5/1935 Dornier170/135.4 2,569,882 10/1951 Bothezat 244/17;25 2,886,261 5/1959 Robertet al. 244/17.25

Primary ExaminerMalcolm F. Hubler AnomeyKarl F. Ross ABSTRACT: Anairborne radar station, hovering at a fixed location above an associatedground station, comprises a supporting section with a gyrostabilizedbody held aloft by helicopter blades and a supported section suspendedfrom that body for independent rotation about a substantially verticalaxis. The coupling between the two sections includes aparallelogrammatic linkage with an upper base secured to (or part of)the body and a lower base rigid with the supported section or securedthereto through an adjustable mounting automatically maintaining theverticality of a suspension shaft for that section. The downdraftgenerated by the swirling rotor blades acts upon adjustable fins on thesupported section to rotate the latter at a rate controlled by agovernor and by signals from the ground station which also includes atracking radar trained upon the airborne station to determine deviationsfrom its assigned position in space, such deviations giving rise tocorrective signals transmitted by short waves to the airborne stationfor altering the attitude of the supporting section and theeffectiveness of its blades by changing the direction of thrust of oneor more jets of compressed air issuing from the tip of each blade. Aradar antenna on the rotating supported section scans the surroundingarea. especially in the region close to the ground, and retransmitsincoming echo signals to receiving equipment at the ground station.

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Attorney AIRBORNE STATION FOR AERIAL OBSERVATION SYSTEM for exploring,e.g. by radar, the surrounding terrain and the I area immediately aboveit. Such systems are useful, for example, to guard against sneak attacksby low-flying aircraft or missiles.

The use of lighter-than-air vehicles, such as blimps or barrageballoons, as airborne observation stations has the disadvantages ofbulky and costly equipment, vulnerability to hostile attack and lack ofstability in the face of atmospheric disturbances. If cables are used tohold an airship in a fixed position above the ground, its maximumaltitude is limited to several hundred meters; also, the cables tend tointerfere with the radar beam so as to create blind spots in itspanoramic sweep. On the other hand, the placement of an airborne stationaboard a moving craft creates considerable problems of plotting thelocation of detected objects and of maintaining contact with anassociated ground station, this being true even where the craft followsa predetermined course at relatively low speed and is being continuouslytracked by Doppler-type radar equipment.

The general object of our present invention, therefore, is to provide animproved observation system of the character set forth in which theaforestated disadvantages are avoided.

A more particular object is to provide, in such a system, an airbornestation adapted to hover in a virtually fixed position, at an altitudeon the order of kilometers, above an associated ground station inconstant communication therewith.

It is also an object of our invention to provide means for continuouslyrotating an equipment-bearing section of such an airborne station abouta substantially vertical axis and for maintaining the verticality ofthat axis even under adverse atmospheric conditions, such as gale windsand strong gusts.

These objects are realized, pursuant to our present invention, by theprovision of an aerodyne-type craft divided into a supporting sectionand a supported section, the latter being suspended from the former withfreedom of independent rotation about a substantially vertical axis; thesupporting section carries orientable propulsion means, such as a rotorhaving propeller blades with adjustable nozzles for the discharge ofjets of a high-pressure fluid (preferably air) from their tips, wherebythe attitude of this section can be controlled in response to commandsignals from the ground station to nullify deviations from its assignedlocation as detected by tracking equipment on the ground. Such trackingequipment may include an emitter of continuous or pulsed radar signalsdirected toward a transponder aboard the craft, the latter beingadvantageously positioned substantially at the center of gravity of thesupported section so as to indicate precisely, by Doppler etTect andangle measurements, any displacement of that center (and therefore ofthe axis of rotation of the equipmentcarrying section) as well as,advantageously, the rate of such displacement. The positionalinformation received by the tracking radar is then evaluated by acomputer at the ground station which, via a ratio link of the UHF or VHFtype, transmits corrective signals to the airborne station representedby the craft.

According to another important feature of our invention, we provideimpeller means for rotating the supported section of the craft about itssubstantially vertical axis at a rate controlled from the ground stationby way of the aforementioned radio link. In order to avoid the need fora separate power source to generate such rotation, the impeller meansadvantageously may comprise a set of peripheral vanes on the supportedsection positioned in the downwardly directed slip stream of thepropeller blades of the supporting section. By driving these propellerblades through a discharge of highpressure fluid from their tips, asdescribed above, we also avoid the need for a torque compensatordesigned to counteract the reaction otherwise exerted by the rotor uponits supporting body. The latter, therefore, may be convenientlystabilized against rotation by a conventional gyroscope drawingrelatively little energy from the power supply aboard the craft.

A further aspect of our invention relates to the maintenance of thevertical position of the axis of rotation of the supported section ornacelle carrying the observation equipment. Since the supporting sectionmustbe orientable to compensate for drifts so that its own axis will notinvariably be vertical, the two sections should be interconnected by aswing joint permitting relative inclination of their respective axis atleast over a limited angular range. In order to permit a relativelateral shifting of the two axes in response to air pressure, aparallelogrammatic linkage with two parallel bases, i.e. an upper basecoupled to or forming part of the supporting section and a lower basecoupled to or forming part of the supported section, is advantageouslyinserted in tandem with the swing joint. Under normal atmosphericconditions, gravity alone may be depended upon to maintain the axis ofthe suspended nacelle practically vertical. In the presence of severegusts or sustained air currents of extraordinary magnitude, however,means should be provided for automatically reestablishing the desiredhorizontal plane of rotation. Thus, pursuant to a more specific featureof our invention, we provide an adjustable coupling between the lowerbase of the parallelogrammatic linkage and a shaft tiltably mounted onthat base by the aforementioned swing joint. This adjustable couplingmay take the form of at least two extensible connectors, such assolenoids or fluid-actuated jacks, bearing in two substantiallyconjugate planes upon the lower base and a head or other projection onthe shaft'axially spaced from that base. The term "substantiallyconjugate planes refers to a pair of planes which intersect at thecenter of the swing joint and lie approximately at right angles to eachother as well as to the two bases. The extensible connectors may beselectively adjusted, in response to the direction of tilt, by a plumbdetector disposed within the tubular shaft.

The above and other features of our invention will -be describedhereinafter in greater detail with reference to the accompanying drawingin which:

FIG. 1 is an isometric view illustrating diagrammatically systemaccording to the invention, comprising a ground station and twoassociated airborne stations;

FIG. 2 is an elevational view, partly in section, of a craft forming oneof the airborne stations of FIG. I together with a mobile landingplatform therefor;

FIG. 3 is a block diagram showing the components of the ground stationand an associated airborne station in the system of FIG. 1; FIG. 4schematically shows a parallelogrammatic linkage between a supportingand a supported section of an airborne station according to theinvention, this Figure also including a vector diagram illustrating theinterplay of forces acting upon that linkage; I

FIG. 5 is a view similar to FIG. 2, showing a modified airborne stationaccording to our invention;

FIG. 6 is an elevational detail view, partly in section,,of a.

rotor blade and associated elements forming part of the craf of FIG. 2or 5; and j I FIG. 7 is a perspective view, with parts broken away, ofan adjustable coupling for keeping the supported section of the vehicleof FIG. 5 centered on a vertical axis.

In FIG. 1 we have shown two airborne vehicles I and l" hovering atsubstantially fixed locations above an associated ground station IIwhich, as shown, may be a self-propelled vehicle or a trailer mounted onwheels but which for purposes of the following discussion will beconsidered stationary. The two airborne stations I, l" are assumed to bevirtually identi cal, consisting each of a helicopter-type supportingsection 101, I01" and a nacelle-type supported section 102', 102".

The centers of gravity G, G" of sections 102', 102" are maintained atsubstantially fixed locations given by the dimensions x, y, 2',respectively, in a coordinate system x, y, z with a vertical axis z; asillustrated, the elevations z, z" of the two centers G G" above groundmay be identical.

By a tracking system, more fully described hereinafter, the groundstation II detects any deviation Ax, Ay, Az of the center of gravity ofeither craft from its assigned position and transmits corrective signalsto the craft via a respective radio link 103', 103"; these radio linksneed not be strongly directive and may operate on different UHF or VHFfrequencies for the two stations I and I These radio links may alsoconvey information to the ground station on the condition of theairborne equipment (e.g., on the state of the fuel supply aboard thecraft) and, as also more fully described hereinafter, may transmit echopulses picked up by an airborne radar receiver for indicating thelocation of reflecting objects on a panoramic screen or other displaydevice viewable by the ground crew.

The use of two separate airborne stations I, I" enables continuoussurveillance of the surrounding airspace and terrain by overlappingoperations of their respective radars, with alternate servicing of thetwo crafts to replenish their fuel supply and 21 make necessaryadjustments. Such servicing requires the descent of the craft to groundlevel, again under the control of command signals from station 11, andits subsequent return to its assigned position aloft.

Under ideal conditions, in calm weather, the rotor axes A, A" of thepropellers 101', 101" should coincide with the vertical axes Z, Z"passing through the centers of gravity G, G, the propeller blades thengenerating just enough uplift to balance the weight of the craft wherebythe latter is suspended motionless in space (except for a rotation ofthe nacelles 102, 102" about axes Z, 2" as described hereinafter). Inorder to counteract air currents which would cause the craft to driftfrom its assigned position the rotor axis is headed into the wind by anangle sufficient to create a compensatory velocity component. With asubstantially constant rotor speed, the ascent or descent of the craftmay be controlled by changing the effective pitch of the blades; byperiodically varying this effective pitch in the course of a revolution,we may achieve a desired inclination of the rotor axes with reference tothe vertical axes Z, Z". As described in greater detail below, we mayrealize the effect of such variation in pitch by altering the directionof a high-pressure fluid stream issuing from the trailing edge of eachblade.

In FIG. 2 we have shown in greater detail the two sections 101, 102 ofan aerodyne-type craft representing either of the two airborne stationsI, I" of FIG. 1. Supporting section 101 comprises a gyrostabilized body104 rigid with a tubular shaft 105 on which a propeller hub 106 isjoumaled for rotation about axis A. Two hollow blades 107 extendradially from hub 106 and are provided at their tips with swivelableextensions 108 having slots 109 along their trailing edges, these slotsthus forming orientable nozzles for the discharge of jets of air orother fluid admitted under pressure to the interior of the blades in amanner more fully illustrated in FIG. 6. As shown in that Figure, nozzle108 has a tubular stem 110 joumaled in a fluidtight bearing 111 and opentoward the interior of hub 106 which communicates through ports 112 withthe interior of shaft 105. The position of each stem 110, and thus ofthe corresponding nozzle 108, is adjustable by a mechanism here shown tocomprise a lug 113 projecting outwardly from each blade 107 andterminating in a roller riding on an annular swashplate 114 whoseposition relative to the stabilized body 104 is adjustable by theselective actuation of four peripherally equispaced extendableconnectors 115 (only three shown), such as hydraulic or pneumatic jacks,solenoids, or threadedly interengaging and relatively rotatable members.The selective actuation of these connectors 115 enables the swashplate114 to be bodily raised or lowered along axis A or to be inclined withreference thereto at a desired angle. Lug l 13, when contacting a raisedportion of swashplate 114, turns the stem 110 against the force of atorsion spring 117 in a direction lowering the nozzle outlet 109 so asto generate an upward component of thrust. With the swashplate 114 in aninclined position, the orientation of the nozzle outlet will vary fromdownward to upward and vice versa during a 180 rotation of thecorresponding blade 107 with resulting generation of an asymmetricalthrust component to incline the axis Awith reference to the vertical.

In the embodiment of FIG. 2, the shaft terminates in a ball joint 124linking it with another tubular shaft 118 which rises vertically from ahorizontal base 119 forming a parallelogrammatic linkage with a second,lower base 120, the two bases being articulatedly interconnected bythree rigid rods 121, 122, 123; it will be understood that the minimumnumber of such rods is three but that, if desired, a greater numbercould be provided. The lower base is rigid with a nacelle 125 whichhouses the observation and control equipment described hereinafter, thisequipment being indicated diagrammatically in FIG. 2 by a block mountedon a platform 126 which is braced against the bottom and the sides ofthe nacelle housing by shock-absorbing suspension means here shown as aset of springs 127. The nacelle housing is advantageously designed as aradome and should include the necessary electromagnetic shieldingbetween its sensitive equipment and other parts of the craft. Anundercarriage 128, here shown as comprising essentially a tripod, isdesigned to facilitate a soft landing of the craft on the ground. A setof peripheral vanes 129, of adjustable pitch angle, extend peripherallyfrom the nacelle 125 so as to set the latter in rotation about thevertical axis Z passing through the center of gravity of the nacelle,this rotation being caused by the downdraft forming part of theslipstream of the propeller blades 107. With the supporting body 104held substantially nonrotating by its internal gyroscopic mechanism, thepitch of the vanes 129 is advantageously so chosen that the sense ofrotation of nacelle 125 is opposite that of propeller 106-108.

In principle, the powerplant driving the propeller may be located eitheron the supporting section 101 or on the supported section 102. In theembodiment of FIG. 2 this powerplant is carried on the nacelle 125 andcomprises a pair of symmetrically disposed air compressors whose outputis delivered through respective pipes 171 to the interior of shaft 118communicating with the interior of shaft 105. Each compressor 140 isdriven by an associated prime mover 141, e. g. a Diesel engine or aturbojet, which also drives a main generator 152 supplying current toall the electric equipment aboard the craft.

If power should fails, e.g. because of exhaustion of the fuel supply forthe engines 141 aboard the craft, the drive of the rotor 106-108 willstop and the craft will start descending. This descent will set theblades 107 in reverse rotation which, through a pinion 143 meshing witha set of teeth 144 (FIG. 6) on hub 106, drives an auxiliary generator145 by way of a unidirectional clutch not shown. This low-powergenerator, besides exerting a braking effect on the propeller to slowdown the descent, also provides an emergency supply of electric currentto keep at least some of the equipment (e.g. the gyroscopic stabilizerof body 104) in operation .and to maintain some communication with theground. In normal use, however, the craft will be brought down by acontrolled descent while there is still enough fuel aboard to drive thepropeller, e.g. after an operating period of 5 to 10 hours.

The construction of the undercarriage 128 and of the nacelle itself maybe simplified by the provision of a mobile platform 146, FIG. 2, whichmay be rolled under the nacelle as the craft hovers at low altitudeabove the ground and which is shown to comprise a cradle 147 supportinga spherically convex rocker member 148 whereon a disk 149 is freelyrotatable about a shaft 150. Thus, the craft may alight on the platform146 with the nacelle 125 still rotating and with its undercarriage 128inclined at a small angle relative to the horizontal.

In FIG. 3 we have used the same reference numerals as before to indicateelements already described (or their equivalent). These elements includethe block 130 of FIG. 2, here shown as a rectangle, as well as the mainand auxiliary current generators 142, 145, the powerplant 141, thepropeller drive 140 (represented by the compressors of FIG. 2), the gyrostabilizer 104, and the attitude control represented in FIGS. 2 and 6 bythe jacks 115. There is also provided a fuel reservoir 151 which mayinclude a conventional floatttype level indicator, not shown, fortransmitting information on its contents to the block 130 fortransmission to ground station 11.

For the sake of clarity, we have indicated mechanical connections inFIG. 3 by dot-dash lines, power circuits by heavy solid lines andsignaling circuits by thin solid lines.

The equipment forming part of block 130 includes a radar transmitter 31with a directive antenna 30 also connected to an associated radarreceiver 32. An omnidirectional antenna 341, associated with atransceiver 34, forms part of the radio link 103 described in connectionwith FIG. 1. Transceiver 34, coupled with radar transmitter 31 andreceiver 32 for exchanging information therewith, also works into acommand generator 35 delivering output signals to an automatic pilot 33and to a governor 17 connected via a mechanical linkage 18 with thevanes 129. Governor 17 may be basically a centrifugal speed regulatoradjustable under the control of signals from command generator 35; ifdesired, however, the centrifugal regulator may be omitted and thegovernor may respond only to the command signals received via radio link103 and generator 35.

The autopilot 33, on the basis of the drift information Ax, Ay, Azsupplied to it from command generator 35, sets the attitude control 115to reorient the nozzles of flaps 108 as described above. These driftsignals Ax, Ay, Az are derived from a computer 43 on the ground whichreceives positional information from a tracking radar including atransceiver 45 with directive antenna 44 and a plotter 46 evaluating theoutput of the transceiver as is well known per se. The radiation patternof antenna 44 may be a relatively narrow cone trained upon the generallocation of the center of gravity of nacelle 125 which is assumed todeviate only slightly from its assigned position. This center of gravitysubstantially coincides with an aerial 371 of a transponder 37 aboardthe craft 1, cooperating with the antenna 44 of the tracking radar, sothat plotter 46 can determine at any instant the drift, if any, of thenacelle from a fixed reference point having the coordinates x, y, 2.Computer 43 then generates the magnitudes AI, Ay, A2 of the correctivesignals which, via a transceiver 40 with antenna 401 forming part of theradio link 103, retransmits them to the craft 1. 7

Radar pulses picked up by antenna 30 in nacelle 125 are transmitted viathe same radio link to a video stage 41 whose output appears on adisplay indicator 42, such as an oscilloscope screen. Indicator 42 issynchronized with the rotation of nacelle 125, and therefore with thesweep of scanning antenna 30, by timing pulses from a clock circuit 152which also reach a scan-control network 153 connected in the output of amonitoring receiver 154. A sharply directive antenna 155 of receiver 154detects, once per revolution of nacelle 125, a continuous beam 156transmitted by an eccentrically positioned antenna 157 aboard the craft,this antenna forming part of a transmitter 158. The control network 153delivers to computer 43 a signal representative of the speed of rotationof nacelle 125, thereby enabling this computer to transmit to commandgenerator 35 other corrective signals acting upon speed governor 17 tokeep the antenna sweep synchronized with the operation of indicator [4.

In FIG. 4 we have diagrammatically illustrated a parallelogrammaticlinkage with upper and lower bases 119 and 120, such as the oneillustrated in FIG. 2, suspended from a fixed point 0 (such as thecenter of the ball joint 1240f FIG. 2) and supporting a load, such asthe nacelle 125, having a center of gravity G. in the vertical positionof the linkage, points G and 0 lie on a common axis Z representing theaxis of rotation of the nacelle. The downwardly directed force p,representing gravity (together with a possible vertical acceleration),is then exactly balanced by an upward force q representing the upliftgenerated by the swirling propeller.

If, now, a lateral force f (due, for example, to a squall) acts upon thecenter 0, the linkage is deflected into a position partly illustrated indotted lines in which, however, the

' resultant r is no longer in line with the point 0. This resultant rhas two components r, and r the former being on a line L passing through0 while the latter is perpendicular to that line and generates a torque(here clockwise) centered on 0. Whereas the force r can be compensatedby a corresponding inclination of the vector q through a change of thepropeller attitude, the component r, can be balanced only by areorientation of the parallelogrammatic linkage, i.e. a transition fromthe unstable dotted line position to a stable position illustrated indot-dash lines. In the latter position the bases 119 and 120 are nolonger horizontal, yet the resultant r of forces p and f now coincideswith line L passing through the suspension point 0, the balancing forceq 4 being then exactly equal and opposite to vector r.

With the arrangement heretofore described, in which the nacelle wasrigid with lower base 120, the horizontal position of platform 126 (FIG.2) could therefore not be maintained in the face of squalls or strongwinds giving rise to an appreciable deflecting force f. For this reason,in a modified system more fully described hereinafter with reference toFIG. 5, we have shown in FIG. 4 an articulated suspension for thenacelle including a shaft 159 swingable about a ball joint 160 on base120. Since the swing joint at point 0 now becomes redundant, we mayconnect the stabilized supporting body 104 rigidly with shaft 1 18rising from base 119.

Since, under the assumed condition of strong atmospheric disturbances,gravity alone could not be relied upon to keep the nacelle from swaying,we provide an adjustable coupling between the shaft 159 and the base 120in the form of a projection 161 on the shaft and an extensible connector162, similar to the elements 115 of FIGS. 2 and 6, anchored to thatprojection and to the base 120. In the swung-out position illustrated indot-dash lines, the connector 162 is automatically extended to restorethe vertical position of shaft 159. The manner in which this is donewill be described in greater detail with reference to FIGS. 5 and 7.

The supporting section 101a of the modified craft la shown in FIG. 5 isgenerally similar to section 101 of FIG. 2 and need not be described indetail, except for the fact that shaft 118 has been extended upwardly toreplace shaft 105 and that the power supply units 140-142 have beenrelocated on the upper base 119 of the parallelogrammatic linkage,within a protective canopy 163, the gyrostabilized body 104 being nowrigid with shaft 118 and with platform 119. On the other hand, nacelle125 is rotatably suspended from shaft 159 through a bearing 164 alsoestablishing, via one or more sliprings 165 and contact brushes 166,electrical continuity between sections 101a and 102a. It will beunderstood that these sliprings and brushes are connected to insulatedwires extending within the shaft 159 and the suspending framework 167; acable extending partly within shafts 118 and 159 encompasses a portionof this circuit.

The aforedescribed swing joint between shaft 159 and base 120 comprisesa ball 168 on the shaft held in a spherically curved ring socket 169which is rigid with base 120. The jack 162 of FIG. 4 is representativeof two such jacks 162x, 162y bearing upon a head 161 (FIG. 5) above base120, or upon a pair of arms 161x, 16ly (FIG. 7) below that basesymbolized by the similarly designated projection of FIG. 4; the twojacks thus serve to swing the shaft 159 in two mutually conjugate planeswhich may be respectively parallel to the x2. plane and the yz plane ofthe coordinate system of FIG. 1.

As more particularly illustrated in FIG. 7, the interior of shaft 159contains a plumb detector in the form of a conductive weight 172suspended from a wire 173, this weight being out of contact with a setof conductive segments 174 on the in.- side of the nonconductive orinsulation-lined shaft 159 as long as the latter is substantiallyvertical. As soon as the shaft tilts in any direction, weight 172engages one of the segments I74 and closes a circuit to a controllerinside the bass 168 which energizes either or both jacks 162x, 162y inan extending and/or contracting sense to restore the shaft to itsvertical position.

The nacelle 125 may, of course, be provided with any conventionalsupplemental equipment needed to ensure satisfactory operation,including protective screening against cosmic radiation. The platform146 illustrated in FIG. 2 may be used for both landing and takeoff, thussewing as aconvenient means for initially positioning the craft 1 inline with its desired airborne location. Naturally, compatible featuresfrom different embodiments (e.g. the provision of a protective canopy163, FIG. 5, for the assembly 140-142 of FIG. 2) may be combined orsubstituted without departing from the spirit and scope of ourinvention.

We claim:

1. An aerial observation system comprising a ground station; an airbornestation hovering above said ground station at a substantially fixedlocation, said airborne station including a supporting section providedwith orientable propulsion means for holding same aloft and furtherincluding a supported section suspended from said supporting sectionwith freedom of at least limited relative inclination and independentrotation about a vertical axis; a radio link interconnecting saidstations; tracking means at said ground station for detecting deviationsof said airborne station from a predetermined position in space;evaluation means at said ground station coupled to said tracking meansfor translating such deviations into corrective signals and fortransmitting same to said airborne station via said radio link; controlmeans at said airborne station coupled to said radio link forreorienting said propulsion means in response to said corrective signalsto nullify said deviations; impeller means for rotating said supportedsection about said axis; observation equipment aboard said supportedsection for exploring the space around said airborne station andtransmitting resulting information signals to said ground station by wayof said radio link; receiving means at said ground station coupled tosaid radio link for directing said information signals to a load;sensing means aboard said airborne station responsive to tilting of saidsupported section with reference to said axis; and control means coupledto said sensing means for angularly adjusting said supported section torestore the verticality thereof.

2. A system as defined in claim 1 wherein said propulsion meanscomprises a rotor with a generally vertical axis having a set of bladesand drive means for rotating said blades about the rotor axis.

3. A system as defined in claim 2 wherein said blades have tips providedwith adjustable nozzle means, said drive means including a source ofhigh-pressure fluid led to said nozzle means for discharge into theatmosphere, said control means comprising a mechanism for adjusting saidnozzle means.

4. A system as defined in claim 2 wherein said impeller means comprisesa set of peripheral vanes on said supported section adjustable disposedin the slipstream of said blades for rotation thereby.

5. A system as defined in claim 4, further comprising governor meanscontrollable from said ground station via said radio link for varyingthe speed of rotation of said supported section by adjusting said vanes.

6. A system as defined in claim 2, further comprising generator meanscoupled with said rotor for entrainment thereby upon reverse rotation ofsaid blades to supply emergency power to said airborne station upon anuncontrolled descent of the latter.

7. A system as defined in claim 2 wherein said sections are providedwith a swing joint interconnecting same with freedom of relativeinclination in different vertical planes.

8. A system as defined in claim 7, further comprising aparallelogrammatic linkage interconnecting said sections in tandem withsaid swing joint for permitting limited relative lateral shifting ofsaid axes.

9. A system as defined in claim 8 wherein said supporting sectioncomprises a rotor-carrying body and said linkage includes an upper baserigid with said body and a lower base parallel to said upper base, saidsupported section comprising a nacelle rotatable with reference to saidbody.

10. A system as defined in claim 9 wherein said nacelle has a shafttiltably mounted on said lower base by said swing joint, furthercomprising an adjustable coupling between said lower base and saidshaft, said sensing means including a detector on said shaft forascertaining departures thereof from a vertical position, said controlmeans including automatic means for adjusting said coupling under thecontrol of said detector means to restore said vertical position.

1 1. A system as defined in claim 10 wherein said adjustable couplingcomprises a projection on said shaft axially spaced from said lower baseand a pair of extensible connectors eccentrically linking saidprojection with said lower base in two substantially conjugate planes.

12. A system as defined in claim 9 wherein said supported sectionfurther includes an instrument-carrying platform and cushioning meansyieldably supporting said platform in said nacelle.

13. A system as defined in claim 9 wherein said nacelle is provided withan undercarriage for landing on the ground, further comprising a mobilecradle on the ground and a rotatable rocker on said cradle forming analighting surface for said undercarriage.

14. A system as defined in claim 1 wherein said observation equipmentcomprises a radar antenna positioned to explore the area surroundingsaid airborne station.

15. A system as defined in claim 1 wherein said tracking means comprisesradar equipment at said ground station and a transponder aboard saidairborne station located substantially at the center of gravity of saidsupported section.

16. A system as defined in claim 1, further comprising a second airbornestation hovering above said ground station at another substantiallyfixed location, said airborne stations being substantially identical foroverlapping utilization under the control of said ground station wherebyobservation can be carried out continuously during alternate servicingof said airborne stations.

17. An aerial observation system comprising a ground station; anairborne station hovering above said ground station at a substantiallyfixed location, said airborne station including a supporting sectionprovided with orientable propulsion means for holding same aloft andfurther including a supported section suspended from said supportingsection with freedom of at least limited relative inclination, saidsupported section comprising a rotatable nacelle provided with anundercarriage; a radio link interconnecting said stations; trackingmeans at said ground station for detecting deviations of said airbornestation from a predetermined position in space; evaluation means at saidground station coupled to said tracking means for translating suchdeviations into corrective signals and for transmitting same to saidairborne station via said radio link; control means at said airbornestation coupled to said radio link for reorienting said propulsion meansin response to said corrective signals to nullify said deviations;impeller means for rotating said nacelle about a substantially verticalaxis; observation equipment on said nacelle for exploring the spacearound said airborne station and transmitting resulting informationsignals to said ground station by way of said radio link; receivingmeans at said ground station coupled to said radio link for directingsaid information signals to a load; a mobile cradle on the ground; and arotatable rocker on said cradle forming an aligning surface for saidundercarriage.

1. An aerial observation system comprising a ground station; an airbornestation hovering above said ground station at a substantially fixedlocation, said airborne station including a supporting section providedwith orientable propulsion means for holding same aloft and furtherincluding a supported section suspended from said supporting sectionwith freedom of at least limited relative inclination and independentrotation about a vertical axis; a radio link interconnecting saidstations; tracking means at said ground station for detecting deviationsof said airborne station from a predetermined position in space;evaluation means at said ground station coupled to said tracking meansfor translating such deviations into corrective signals and fortransmitting same to said airborne station via said radio link; controlmeans at said airborne station coupled to said radio link forreorienting said propulsion means in response to said corrective signalsto nullify said deviations; impeller means for rotating said supportedsection about said axis; observation equipment aboard said supportedsection for exploring the space around said airborne station andtransmitting resulting information signals to said ground station by wayof said radio link; receiving means at said ground station coupled tosaid radio link for directing said information signals to a load;sensing means aboard said airborne station responsive to tilting of saidsupported section with reference to said axis; and control means coupledto said sensing means for angularly adjusting said supported section torestore the verticality thereof.
 2. A system as defined in claim 1wherein said propulsion means comprises a rotor with a generallyvertical axis having a set of blades and drive means for rotating saidblades about the rotor axis.
 3. A system as defined in claim 2 whereinsaid blades have tips provided with adjustable nozzle means, said drivemeans including a source of high-pressure fluid led to said nozzle meansfor discharge into the atmosphere, said control means comprising amechanism for adjusting said nozzle means.
 4. A system as defined inclaim 2 wherein said impeller means comprises a set of peripheral vaneson said supported section adjustable disposed in the slipstream of saidblades for rotation thereby.
 5. A system as defined in claim 4, furthercomprising governor means controllable from said ground station via saidradio link for varying the speed of rotation of said supported sectionby adjusting said vanes.
 6. A system as defined in claim 2, furthercomprising generator means coupled with said rotor for entrainmentthereby upon reverse rotation of said blades to supPly emergency powerto said airborne station upon an uncontrolled descent of the latter. 7.A system as defined in claim 2 wherein said sections are provided with aswing joint interconnecting same with freedom of relative inclination indifferent vertical planes.
 8. A system as defined in claim 7, furthercomprising a parallelogrammatic linkage interconnecting said sections intandem with said swing joint for permitting limited relative lateralshifting of said axes.
 9. A system as defined in claim 8 wherein saidsupporting section comprises a rotor-carrying body and said linkageincludes an upper base rigid with said body and a lower base parallel tosaid upper base, said supported section comprising a nacelle rotatablewith reference to said body.
 10. A system as defined in claim 9 whereinsaid nacelle has a shaft tiltably mounted on said lower base by saidswing joint, further comprising an adjustable coupling between saidlower base and said shaft, said sensing means including a detector onsaid shaft for ascertaining departures thereof from a vertical position,said control means including automatic means for adjusting said couplingunder the control of said detector means to restore said verticalposition.
 11. A system as defined in claim 10 wherein said adjustablecoupling comprises a projection on said shaft axially spaced from saidlower base and a pair of extensible connectors eccentrically linkingsaid projection with said lower base in two substantially conjugateplanes.
 12. A system as defined in claim 9 wherein said supportedsection further includes an instrument-carrying platform and cushioningmeans yieldably supporting said platform in said nacelle.
 13. A systemas defined in claim 9 wherein said nacelle is provided with anundercarriage for landing on the ground, further comprising a mobilecradle on the ground and a rotatable rocker on said cradle forming analighting surface for said undercarriage.
 14. A system as defined inclaim 1 wherein said observation equipment comprises a radar antennapositioned to explore the area surrounding said airborne station.
 15. Asystem as defined in claim 1 wherein said tracking means comprises radarequipment at said ground station and a transponder aboard said airbornestation located substantially at the center of gravity of said supportedsection.
 16. A system as defined in claim 1, further comprising a secondairborne station hovering above said ground station at anothersubstantially fixed location, said airborne stations being substantiallyidentical for overlapping utilization under the control of said groundstation whereby observation can be carried out continuously duringalternate servicing of said airborne stations.
 17. An aerial observationsystem comprising a ground station; an airborne station hovering abovesaid ground station at a substantially fixed location, said airbornestation including a supporting section provided with orientablepropulsion means for holding same aloft and further including asupported section suspended from said supporting section with freedom ofat least limited relative inclination, said supported section comprisinga rotatable nacelle provided with an undercarriage; a radio linkinterconnecting said stations; tracking means at said ground station fordetecting deviations of said airborne station from a predeterminedposition in space; evaluation means at said ground station coupled tosaid tracking means for translating such deviations into correctivesignals and for transmitting same to said airborne station via saidradio link; control means at said airborne station coupled to said radiolink for reorienting said propulsion means in response to saidcorrective signals to nullify said deviations; impeller means forrotating said nacelle about a substantially vertical axis; observationequipment on said nacelle for exploring the space around said airbornestation and transmitting resulting information signals to said groUndstation by way of said radio link; receiving means at said groundstation coupled to said radio link for directing said informationsignals to a load; a mobile cradle on the ground; and a rotatable rockeron said cradle forming an aligning surface for said undercarriage.